1. Field of the Invention
This invention relates to a display apparatus for a vehicle, installed in a dashboard of the vehicle and displays a virtual image of information of the vehicle within a field of front view of a vehicle driver by projecting the information of the vehicle displayed on an image plane of an LCD illuminated by a lighting device on a windshield or a combiner disposed at an outside of the dashboard.
2. Description of the Related Art
This kind of the display apparatus for the vehicle, called a head up display (HUD), is applied to display auxiliary information for driving in a filed of a front view, as disclosed in J.U.M Application Laid-open H4-54020, and has a feature to recognize auxiliary information without moving eye point during driving.
FIG. 28 shows an outline drawing of a usual display apparatus for the vehicle as mentioned above. A virtual image 10 of a speed meter is displayed on a windshield 2 located above an instrument panel 2a of a vehicle 1.
FIG. 29 shows a structure for displaying the virtual image 10. The instrument panel 2a is provided inside thereof with a convex lens 5, LCD (Liquid Crystal Display) 3, a light source 6 and an LCD drive circuit 4. The LCD 3 is disposed on a focal point of the convex lens 5. The light source 6 is disposed behind a semi-transparent mirror 12 at opposite side against the convex lens 5 regarding the LCD 3.
The LCD 3 includes a display plate 3a, a negative-positive image switching plate 3b and a polarizing plate 3c. The LCD 3 is connected to the LCD drive circuit 4 connected to a car speed sensor 13.
The light source 6 has a high brightness lamp 6a and a low brightness lamp 6b those are separated by the semi-transparent mirror 12 in a lamp case 14. Each light of the lamps 6a, 6b enters respectively from a bottom side of the LCD 3 into the convex lens 5 by the semi-transparent mirror 12. A negative-positive image select switch 15 is connected between the negative-positive image switching plate 3b and the LCD drive circuit 4. A lamp select switch 16 is connected between the high brightness lamp 6a and the low brightness lamp 6b. The both select switches 15, 16 are switched interlockingly with a side lamp switch 17 of the vehicle.
According to above structure, a display image Q is generated on the LCD 3 by converting a signal of the car speed sensor 13 to an LCD drive signal in the LCD drive circuit 4. A polarizing direction of the polarizing plate 3c attached on the bottom side of the LCD is selected so as to show the display image Q by a negative image in the field of the front view as FIG. 30A. In the daytime, the high bright lamp 6a is turned ON at the same time when the LCD displays an image. Light of the high brightness lamp reflected in the lamp case 14 is reflected at the semi-transparent mirror 12 to illuminate the display image Q of the LCD 3 and goes through the convex lens 5. The light is reflected on the windshield 2 so as to display the negative image (virtual image 10) in the front view as shown in FIG. 30A.
In the nighttime, the side lamp 17 is turned ON and the light source 6 is selected to the low brightness lamp 6b by the lamp select switch 16. Simultaneously, the negative-positive image select switch 15 is turned ON and the virtual image 10 in the front view is switched to the positive image as shown in FIG. 30B. This selection of images is done by driver's judgement.
Objects to be Solved
The head up display is required to select display only for nighttime other than common display for daytime and nighttime. The display only for nighttime may be an image by a night vision camera or an image processed the image by the night vision camera. When such image is displayed, a display condition, such as a display size or display brightness, may be different from the common display (for daytime) preferably to be seen easily by the driver.
In the above-mentioned usual display apparatus for a vehicle, the display size of the virtual image in the front view is the same in the daytime and the nighttime, and cannot change the display size as occasion demands.
To overcome the above drawback of a usual display apparatus for a vehicle, one object of this invention is to provide a display apparatus for a vehicle which can change a display condition to display information for driving in a field of a front view of a vehicle driver.